1. Field of the Invention
This invention relates to a circulating type ball spline bearing employing a cylindrical race body which has both load carrying ball raceways in U-shaped channels and non-load carrying ball grooves radially cut into its inner periphery in such a manner that a contact angle on an extension line connecting a load carrying ball with a non-load carrying ball lies as close to the torque direction as possible.
In the circulating type ball spline bearing, the balls which are accommodated in the outer sleeve or race body of the bearing are engaged with and put in smooth rolling motions in guide tracks of the spline shaft, permitting torque transmission and ensuring light and smooth movements even in a preloaded state without frictional wear of sliding parts. Therefore, it is suitable for application to those machines which requires high positioning accuracy as well as repeated accuracy and rigidity, for example, machining centers, X-Y-Z guides of various NC machine tools, electric discharge machines, high speed presses, high precision press ram guides, press die exchangers and a diversity of weight transfer mechanisms.
2. Description of Prior Art
As indicated by imaginary lines a and b in FIG. 2, the conventional ball spline bearing has the non-load carrying ball groove b located on the extension of a line which connects the center of the outer sleeve with the center of a load carrying ball so that it has to be formed in a large diameter a, requiring a high material cost and imposing restrictions on the design of the machine on which the bearing is to be used. In addition, it is subjected to great inertial force during rotation of the ball spline, giving rise to problems with regard to the strength of the shaft itself.
In an attempt to eliminate the above-mentioned drawbacks or problems, the present inventor developed prior to this invention a circulating type ball spline bearing which has the non-load carrying ball grooves formed in the outer sleeve at a position on the extension of a line connecting a load carrying ball with a R-groove of the spline shaft and a line connecting the load carrying ball with the non-load carrying ball to have its contact angle as close to the torque direction as possible, thereby increasing the torque transmission.
However, it has been found extremely difficult to form a plural number of non-load carrying grooves through the outer sleeve by boring operation due to its limited thickness, the efficiency of the boring operation being often impaired by abrasion or damage of drills or other tools.